[backport] Comments in versions.properties

Backport of f915361

Author: lrytz

versions.properties

@@ -3,13 +3,19 @@
 # via scala-dist-pom.xml and scala-library-all-pom.xml
 # when adding new properties that influence a release,
 # also add them to the update.versions mechanism in build.xml,
-# which is used by scala-release-2.11.x in scala/jenkins-scripts
+# which is used by the release script scripts/jobs/integrate/bootstrap
+
+# The scala version used for boostrapping. This has no impact on the final classfiles:
+# there are two stages (locker and quick), so compiler and library are always built
+# with themselves. Stability is ensured by building a third stage (strap).
 starr.version=2.11.6
 
 # These are the versions of the modules that go with this release.
 # These properties are used during PR validation and in dbuild builds.
 
-# e.g. 2.11.0-RC1, 2.11
+# The scala.binary.version determines how modules are resolved. After 2.x.0 is released,
+# the binary version is 2.x. For milestones and RCs, modules are cross-built against the
+# full version, so the value, so the value is the full version (e.g. 2.12.0-M1).
 scala.binary.version=2.11
 # e.g. 2.11.0-RC1, 2.11.0, 2.11.1-RC1, 2.11.1
 # this defines the dependency on scala-continuations-plugin in scala-dist's pom